The present invention relates to a process for fabricating a semiconductor device. In particular, it relates to treatment of the surface of a metal layer exposed by dry etching part of a phosphosilicate glass (PSG) layer covering the metal layer, the exposed metal layer being used for an electrical connection.
Many semiconductor devices having various types of circuit elements formed in a semiconductor substrate, include a metal interconnection layer which connects an impurity doped layer, a gate electrode, or another component in the substrate, to the exterior of the substrate or to another circuit element in the substrate. Such a metal interconnection layer is often covered with a PSG layer as a protective layer or an insulating layer between metal layers. Such a PSG layer covering a metal layer is partly removed by etching so as to expose the underlying metal layer and to form a connection between the exposed area of the metal layer and the exterior or another circuit element of the substrate.
Recently, dry etching processes such as parallel plane-type plasma etching, ion beam etching, sputter etching, and so on have been used for etching PSG layers in order to increase the processing precision, simplify the treatment, or accomplish other purposes. However, a metal layer exposed by dry etching a PSG layer covering the metal layer may result in an insufficient electrical connection or may increase the contact resistance when a wire is bonded onto it or a connection is made to it. If such an exposed metal surface is used as an electrode pad for wire bonding, the metal of the wire does not sufficiently alloy with the metal of the pad, sometimes resulting in separation of the wire from the pad. If a second metal layer is deposited on an insulating PSG layer covering a first metal layer as well as in a through hole formed by dry etching part of the PSG layer, i.e., the exposed area of the first metal layer, the contact between the two metal layers may not be electrically sufficient and may result in a disconnection with the passage of time.
It has been proposed to treat the surface of a metal layer with a hydrofluoric acid solution, etc. after exposing by dry etching a silicon dioxide (SiO.sub.2) layer covering the metal layer. However, this method is not very effective and, in addition, concerns a SiO.sub.2 layer, not a PSG layer.